This invention relates to the composition, synthesis, and use of one-component substantially solvent-free aqueous polyurethane-urea dispersion.
Polyurethane dispersions have been used in a wide range of commercial applications such as ink, adhesives and coatings for various substrates including textile fabrics, plastic, wood, glass fibers and metals. Chemical resistance, abrasion resistance, toughness, tensile strength, elasticity and durability are among the many desirable properties of these coatings. Polyurethane polymers generally contain urethane groups, and urea groups in their backbone structure. They are typically formed by the reaction of a diisocyanate with a polyol or polyamine.
Conventionally, coatings and adhesive of polyurethane have been formed from solutions of the polyurethane in organic solvents. As the coating and adhesive cure, the solvents evaporate into the atmosphere. This is economically disadvantageous due to the high costs of these solvents, but more importantly, these solvents also cause pollution of the atmosphere and health hazard to people handling the products. Solvent-based polyurethane face ever-tightening health and environmental legislation aimed at reducing volatile organic compound (VOC) and hazardous air pollutant emissions. Accordingly, alternatives to conventional solvent-based products are needed. Some efforts have been directed to polyurethane coatings and adhesive from dispersions of these polymers in water. Economically, the use of water is very advantageous and, in addition, water does not pollute the atmosphere when it evaporates from the coating and adhesive.
Related disclosures include U.S. Pat. No. 2,968,575, U.S. Pat. Nos. 3,905,929, 3,920,598, 4,408,008; 5,270,433; 7,294,670; 4,387,181; 5,563,208; 6,586,523; 5,703,193 and 7,242,068 and U.S. Patent Application Publication Nos. 2006/0241228 A1 and 2003/0220463 A1.
Polyurethane adhesives are being increasingly used in the manufacture of electronic devices. In such devices, the application of the adhesive, specific bonding process and electrical properties of the material are increasingly becoming important to the overall performance and lifetime of the electronic device. The adhesive typically should perform similarly at one condition after being exposed to different conditions. For example, a device such as a display device that shows good contrast ratio and switching times at 25° C. and 80 percent relative humidity should have the same performance when returned to this condition after being exposed to high or low temperatures and humidity for short periods of time. This requirement necessitates that the adhesive electrical properties and adhesion are not altered by exposure to these conditions. Without being bound by theory, it is believed that the electrical properties of the adhesive, specifically volume resistivity and/or conductivity, are related to the materials ability to be ionically conductive.
There are many patents and descriptions of such adhesive materials that are used in electronic devices that demonstrate certain adhesive and electrical properties. However, most of these materials refer to curable systems that are filled with conductive media. Relatively few references to non-curable adhesives are provided.
Thus, to overcome one or more of the deficiencies of the related art, it would be desirable to provide new aqueous polyurethane dispersions and processes of making them.